(A) study on the residual stress in thermal processing by the arc and laser beam

Abstract

The transient thermal stress and residual stress in bead-on-plate welding and laser surface hardening were analyzed by employing a new two-dimensional finite element model. Inthe formulation, the sliced solution domain posssessing one element in the welding or hardening direction was introduced to allow the change of the longitudianl total strain along the width and depth of the specimen. The longitudinal total strain, which makes the resultant force in the longitudinal direction to be zero, was used as the boundary condition. To determine the longitudinal total strain, the equations of the compatibility, force equilibrium and moment equilibrium were considered. Calculation of the transient temperature distribution was based on the two-dimensional finite element model of the quasi-stationary condition. By using the proposed model the thermal and residual stresses fo the bead-on-plate GTA welding was successively calculated. The computed results were compared with those by the conventional two-dimensional model of the plane strain condition. The simultion results revealed that the present model could more reasonably describe the thermal and residual stresses than the palne strain model. The thermal and residual stresses in the laser surface hardening treatment was also successively calculated. The thermal stress was induced mainly from the temperature gradient and martenstic phase transformation, which was found to have a greater influence on the residual stress than the former. The simulation results revealed that a compressive residual stress region occurs near the hardened surface of the workpiece and a tensile residual stress region in the interior of the workpiece, while the maximum tensile residual stress occurs along the center of the laser scanning path in the interior region. In the multipass laser surface hardening, the region of the tensile residual stress remains on the hardened surface, if the distrance between the neighbouring passes is larger than...